wait4(2)/waitid(2): separate copying rusage to userland

New helpers: kernel_waitid() and kernel_wait4().  sys_waitid(),
sys_wait4() and their compat variants switched to those.  Copying
struct rusage to userland is left to syscall itself.  For
compat_sys_wait4() that eliminates the use of set_fs() completely.
For compat_sys_waitid() it's still needed (for siginfo handling);
that will change shortly.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 52 insertions, 37 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index f98782bd27b6..d44f12948c5f 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1003,7 +1003,7 @@ struct wait_opts {
 
         struct siginfo __user   *wo_info;
         int __user              *wo_stat;
-        struct rusage __user    *wo_rusage;
+        struct rusage           *wo_rusage;
 
         wait_queue_t            child_wait;
         int                     notask_error;
@@ -1054,8 +1054,10 @@ static int wait_noreap_copyout(struct wait_opts *wo, struct task_struct *p,
                                 pid_t pid, uid_t uid, int why, int status)
 {
         struct siginfo __user *infop;
-        int retval = wo->wo_rusage
-                ? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
+        int retval = 0;
+
+        if (wo->wo_rusage)
+                getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
 
         put_task_struct(p);
         infop = wo->wo_info;
@@ -1182,8 +1184,9 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
                 spin_unlock_irq(&current->sighand->siglock);
         }
 
-        retval = wo->wo_rusage
-                ? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
+        if (wo->wo_rusage)
+                getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
+        retval = 0;
         status = (p->signal->flags & SIGNAL_GROUP_EXIT)
                 ? p->signal->group_exit_code : p->exit_code;
         if (!retval && wo->wo_stat)
@@ -1316,8 +1319,9 @@ unlock_sig:
         if (unlikely(wo->wo_flags & WNOWAIT))
                 return wait_noreap_copyout(wo, p, pid, uid, why, exit_code);
 
-        retval = wo->wo_rusage
-                ? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
+        if (wo->wo_rusage)
+                getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
+        retval = 0;
         if (!retval && wo->wo_stat)
                 retval = put_user((exit_code << 8) | 0x7f, wo->wo_stat);
 
@@ -1377,8 +1381,9 @@ static int wait_task_continued(struct wait_opts *wo, struct task_struct *p)
         sched_annotate_sleep();
 
         if (!wo->wo_info) {
-                retval = wo->wo_rusage
-                        ? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
+                if (wo->wo_rusage)
+                        getrusage(p, RUSAGE_BOTH, wo->wo_rusage);
+                retval = 0;
                 put_task_struct(p);
                 if (!retval && wo->wo_stat)
                         retval = put_user(0xffff, wo->wo_stat);
@@ -1618,8 +1623,8 @@ end:
         return retval;
 }
 
-SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
-                infop, int, options, struct rusage __user *, ru)
+static long kernel_waitid(int which, pid_t upid, struct siginfo __user *infop,
+                          int options, struct rusage *ru)
 {
         struct wait_opts wo;
         struct pid *pid = NULL;
@@ -1687,8 +1692,21 @@ SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
         return ret;
 }
 
-SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
-                int, options, struct rusage __user *, ru)
+SYSCALL_DEFINE5(waitid, int, which, pid_t, upid, struct siginfo __user *,
+                infop, int, options, struct rusage __user *, ru)
+{
+        struct rusage r;
+        long err = kernel_waitid(which, upid, infop, options, ru ? &r : NULL);
+
+        if (!err) {
+                if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
+                        return -EFAULT;
+        }
+        return err;
+}
+
+static long kernel_wait4(pid_t upid, int __user *stat_addr,
+                        int options, struct rusage *ru)
 {
         struct wait_opts wo;
         struct pid *pid = NULL;
@@ -1724,6 +1742,19 @@ SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
         return ret;
 }
 
+SYSCALL_DEFINE4(wait4, pid_t, upid, int __user *, stat_addr,
+                int, options, struct rusage __user *, ru)
+{
+        struct rusage r;
+        long err = kernel_wait4(upid, stat_addr, options, ru ? &r : NULL);
+
+        if (err > 0) {
+                if (ru && copy_to_user(ru, &r, sizeof(struct rusage)))
+                        return -EFAULT;
+        }
+        return err;
+}
+
 #ifdef __ARCH_WANT_SYS_WAITPID
 
 /*
@@ -1744,29 +1775,13 @@ COMPAT_SYSCALL_DEFINE4(wait4,
         int, options,
         struct compat_rusage __user *, ru)
 {
-        if (!ru) {
-                return sys_wait4(pid, stat_addr, options, NULL);
-        } else {
-                struct rusage r;
-                int ret;
-                unsigned int status;
-                mm_segment_t old_fs = get_fs();
-
-                set_fs (KERNEL_DS);
-                ret = sys_wait4(pid,
-                                (stat_addr ?
-                                 (unsigned int __user *) &status : NULL),
-                                options, (struct rusage __user *) &r);
-                set_fs (old_fs);
-
-                if (ret > 0) {
-                        if (put_compat_rusage(&r, ru))
-                                return -EFAULT;
-                        if (stat_addr && put_user(status, stat_addr))
-                                return -EFAULT;
-                }
-                return ret;
+        struct rusage r;
+        long err = kernel_wait4(pid, stat_addr, options, ru ? &r : NULL);
+        if (err > 0) {
+                if (ru && put_compat_rusage(&r, ru))
+                        return -EFAULT;
         }
+        return err;
 }
 
 COMPAT_SYSCALL_DEFINE5(waitid,
@@ -1782,8 +1797,8 @@ COMPAT_SYSCALL_DEFINE5(waitid,
         memset(&info, 0, sizeof(info));
 
         set_fs(KERNEL_DS);
-        ret = sys_waitid(which, pid, (siginfo_t __user *)&info, options,
-                         uru ? (struct rusage __user *)&ru : NULL);
+        ret = kernel_waitid(which, pid, (siginfo_t __user *)&info, options,
+                         uru ? &ru : NULL);
         set_fs(old_fs);
 
         if ((ret < 0) || (info.si_signo == 0))